Transformer Bushings
IEEE/ANSI Standard, COTA 150 – COTA 2050
®
Application
Design
Active Part
Trench bushings, Type COTA, are
designed for application on liquid filled
power transformers and reactors. They
are used to connect the power
transformer or reactor to overhead lines
or exposed bus in either outdoor or indoor
conditions.
The active part of the COTA bushing is constructed of oil-impregnated paper
with layers of aluminum foil. The position of the foil layers is computer
optimized to ensure a homogenous electrical field, radially and axially
controlled, providing extremely high dielectric resistance.
The Trench active part design ensures that COTA bushings will last the life of
your power transformer.
Connection to the transformer winding
leads can be accomplished by one of
three methods:
Housing
Bottom connected via a fixed conductor.
The housing is constructed of a head, outdoor insulator, mounting flange,
ground sleeve (COTA 250 and above) and epoxy or fiberglass insulator,
held together by either a central tube or a fixed conductor. Pre-tensioned
cone spring washers provide mechanical stability over the entire temperature
range, ensuring a leak free bushing with the highest possible mechanical
strength. COTA bushings are sealed exclusively with 0-Ring gaskets and
each bushing is hermetically sealed with its own independent oil reservoir.
The interior of the aluminum castings are painted.
Connected via a copper draw lead
cable(s) supplied with the power
transformer.
Bottom connected via Trench’s all copper
“Split-Conductor” draw lead. (Up to 1300
kV BIL)
The method selected depends on voltage
rating, maximum through current or user
preference. Connection to the power
system is accomplished with an industry
standard threaded top terminal.
Head
The cast aluminum head contains an oil expansion chamber with an oil level
indicator. The design of the head allows the bushings to be shipped and
stored horizontally and mounted as follows:
Applicable Standards
COTA 150 and above draw lead models and fixed conductor models above
COTA 200: vertical to a maximum inclination of 40°.
Trench bushings Type COTA, are
designed to meet or exceed the following
industry standards for liquid filled power
transformer or reactor applications:
For greater inclination, contact Trench for special instructions and limitations.
ANSI/IEEE Standard C57.19.00-2003
IEEE Standard General Requirements
and Test Procedure for Outdoor Power
Apparatus Bushings
ANSI/IEEE Standard C57.19.01-2000
IEEE Standard Performance
Characteristics and Dimensions for
Outdoor Apparatus Bushings
IEEE Standard C57.19.100-R2002
IEEE Guide for Application of Power
Apparatus Bushings
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COTA 150 and above draw
lead models and fixed conductor
models above COTA 200
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COTA 150 and COTA 200
Fixed conductor models:
vertical or horizontal
Outdoor Insulator
The outdoor insulator is either a high-grade electrotechnical
porcelain or an insulator constructed from a explosion-resistant
fiberglass epoxy resin tube with molded silicon-rubber sheds.
Porcelain Insulators
Alternating sheds
The standard porcelain insulator on COTA bushings is ANSI
No.70, light gray. Brown porcelain is available upon request.
One-piece porcelain is standard on COTA 150 though 750 and
optional on COTA 900 and 1175. When the height of the
bushing makes it necessary to use more than one porcelain
element, Trench uses a special gluing procedure developed to
ensure that the porcelain elements will exhibit the same level
of performance as a single porcelain element. On bushing style
COTA 250 and above, the porcelain insulator is cemented to the
mounting flange using special cement and sealed with an
0-Ring gasket. To protect against corrosion, the mounting flange
surface and porcelain that is in contact with the cement is
treated with a special coating, ensuring a trouble free interface.
Porcelain insulator
Portland cement
Mounting flange
O-Ring gasket
Silicone Rubber Insulators
Porcelain insulator
Typical design COTA 250 – COTA 900
Silicone rubber insulators used by Trench are specifically
designed for use on high voltage bushings. These insulators
demonstrate superior electrical and mechanical characteristics
not found in other types of
insulators. The physical
properties
of the silicone rubber
provide many advantages
over conventional porcelain
insulators. The silicone
rubber insulator has
demonstrated superior
performance in earthquake
prone areas.
Fiberglass - reinforced
epoxy resin tube
Silicone rubber sheds
Portland cement
Mounting flange
O-Ring gasket
Silicone Rubber insulator
Typical design COTA 250 and above
Silicone rubber insulator
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Design
Mounting Flange
The mounting flange is a high quality aluminum casting,
machined to exact dimensions, ensuring an excellent seal
between the bushing and the transformer.
Integrated into the mounting flange of COTA bushings through
69 kV are test taps. Above 69 kV the mounting flange is
equipped with a voltage tap.
Sealing cap
Epoxy insulator
Embedded End Shield
(Draw Lead COTA 250 though 1175)
High voltage bushings require an end shield to control the
electrical field strength at the inboard end of the bushing.
Instead of mounting this shield externally, Trench embeds the
shield in the epoxy-resin inboard end insulator. This provides
a more uniform distribution of the electrical forces and
reduces the required clearances. The embedded end shield
provides greater interchangeability with other bushings,
making the Trench COTA bushings the ideal replacement
bushing.
Test Tap
COTA 15O – COTA 35O
Sealing cap
Oil plug
Current Path
Two current path options are available:
Voltage Tap
COTA 550 and above
Fixed conductor
Current path via conductor that is fixed in place and has the
active part wound on the conductor. The fixed conductor is
either solid rod or a tube, depending on the specific bushing
design.
Shatter Resistant Inboard End
Every Trench COTA bushing is offered with a shatter resistant
in-board end insulator. These insulators are less susceptible
to damage from handling. They will not shatter like porcelain
preventing major transformer repair costs. Trench in-board
end insulators have 25 years of proven field experience.
The lower end of the COTA bushings (COTA 200 and below)
are protected by an explosion resistant fiberglass-reinforced
epoxy-resin tube or (COTA 250 and above) by a shatter
resistant cone shaped vacuum molded epoxy resin insulator.
These insulators are designed to be installed during the intank drying process of the active part of the transformer and
can withstand temperatures up to 130°C.
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Draw lead
Current path via the transformer’s cable(s) to a silver-plated
copper terminal through multi spring contacts to the copperalloy top terminal. Or via Trench’s copper “Split-Conductor”
draw lead through multi spring contacts to the copper-alloy
top terminal.
Fixed Conductor
Top Terminal
When a fixed conductor bushing is selected the connection to
the transformer winding leads will be at the bottom of the
bushing. The terminal configuration at the bottom of fixed
conductor bushing will depend on the current rating and/or the
desired application and the requirements of the ANSI/IEEE
Standards.
Unlike other bushing designs, where the top terminal is
threaded onto the bushing, the Trench COTA bushing utilizes
a top terminal that is bolted to the head of the bushing. This
feature eliminates the requirement to check the top terminal
for tightness, increasing reliability and providing a truly
maintenance free bushing.
Draw Lead Cable(s)
When the application is less than 800 amperes, draw lead
cable(s), provided with the transformer, can be used. For
recommendations on selecting the draw lead cable(s) for
COTA bushings refer to the Trench COTA Instruction Manual.
The top terminal is designed to accept either a draw lead
terminal or the Trench’s “Split-Conductor”.
On fixed conductor COTA bushings the top terminal is an
integral part of the bushing’s conductor.
Top terminal
When applying draw lead cable(s) on bushings with a vacuum
molded epoxy resin insulator the embedded end shield
provides for a simple, space-saving assembly without
additional shielding or barriers. Refer to the Trench COTA
Instruction Manual for additional details on this feature.
Lock pin
“Split-Conductor” Super Draw Lead
“Split conductor”
upper part
Historically bushings through 69 kV only offered a draw lead
rating of 400 amps. Today, using the Trench “Split-Conductor”
in COTA bushings you now have draw lead ratings to 3,000
amps. Now almost all, medium power transformers through
100 MVA can have all draw lead bushings. The “SplitConductor” draw lead feature provides increased safety for
personnel, shorter installation times and ensures factory
tested transformer lead connections.
Mounting flange
4 Hex-socket screws M10
with disk spring washers
torque 17 ft.lb. (23 Nm)
For “Split-Conductor” applications the termination of the
transformer or reactor winding leads will be at the bottom of
the bushing. The type of termination required will depend on
the maximum through current, operating voltage and
mounting position. Additional measures (shielding, barriers,
etc.) may be required. Contact Trench for available terminals
and shields for your specific application of the “SplitConductor”.
“Split conductor”
lower part
Epoxy insulator
Bottom terminal
“Split-Conductor” & Top terminal
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Cut Views
Top terminal
Top terminal
Draw lead stud
Oil level indicator
Oil level indicator
Head housing
Head housing
Insulator
Insulator
Active part
Name plate
Active part
Test tap
Voltage Tap
(COTA 550 and above)
Air escape plug
(COTA 1050 and above)
Mounting flange
Mounting flange
Grounding sleeve
Test tap
(COTA 350 and below)
FRP tube
Conductor
Epoxy insulator
Bottom terminal
Typical design COTA 250 – COTA 1175
Draw lead
Typical design COTA 150 & COTA 200
Fixed Conductor
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Quality
Everyone talks about quality; nearly everyone is ISO
9001 certified including Trench but that is not the whole
picture. Quality starts at the beginning, it starts with the
design. When you compare a Trench COTA bushing
with other brands you will find quality design features
not offered by the others. These include O-ring gaskets
instead of flat gaskets, the interior of all castings
painted, easy to read prismatic oil level indicators and
stainless steel test tap caps just to mention a few.
Top terminal
Oil level indicator
Head housing
Quality is the reason Trench offers the only standard
three-year bushing warranty in the business. 85 years
in the bushing business and still growing, Trench, the
quality choice for bushings.
Insulator
Active part
Name plate
Standardization
Voltage Tap
(COTA 550 and above)
Air escape plug
(COTA 1050 and above)
Trench COTA bushings were developed to promote the
concept of “standardization”. The designs detailed in
this catalog will cover nearly 100% of the bushing
requirements for liquid filled power transformers or
reactors rated through 2500 MVA, three-phase, 2050
kV BIL. (Excluding high current bushings for GSU
transformers) All COTA bushings though 900 kV BIL
are designed for operation, without de-rating, to an
altitude of 10,000 feet. COTA bushings above 900 kV
BIL are offered with altitude ratings based on the BIL
rating of the specific bushing. Example; a COTA 1050
may be rated for 10,000 feet while the same bushing
rated at 1300 kV BIL will only be rated for operation at
3,300 feet.
Mounting flange
Grounding sleeve
Test tap
(COTA 350 and below)
COTA bushings (COTA 200 and above) have as
standard, “extra-creep” porcelain in accordance with
the heavy contamination level as described in the IEEE
Guide for Application of Power Apparatus Bushings,
C57.19.100-R2002.
Epoxy insulator
COTA bushings present a level of standardization that
will reduce inventories while meeting the most
demanding requirements.
Bottom Terminal
Typical design COTA 550 and above
Fixed conductor
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C57.19.01-2000
COTA Technical Specification Sheets
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inches)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance. (Inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
150-H015-21-AG2-01
025D001A
draw lead
25
16
1,500
21
150
COTA
150-F027-21-AG2-01
025F002A
fixed
25
16
2,700
21
150
COTA
150-H030-21-DG4-01
025S011A
draw lead
25
16
3,000
21
150
60
50
21
9.25
10,000
gray
40
vertical
60
50
21
9.25
10,000
gray
100
vertical/horizontal
60
50
34.6
13.38
10,000
gray
128
Vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inches)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance. (Inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
200-H015-21-AG3-01
035D001A
draw lead
34.5
22
1,500
21
200
COTA
200-F023-21-AG3-01
035F002A
fixed
34.5
22
2,350
21
200
COTA
200-H030-21-DG3-01
035S013A
draw lead
34.5
22
3,000
21
200
80
75
34.6
13.38
10,000
gray
66
vertical
80
75
34.6
13.38
10,000
gray
115
vertical/horizontal
80
75
34.6
13.38
10,000
gray
128
vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inch)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance (inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
250-H014-21-AG3-01
046D001A
draw lead
46
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1,400
21
250
COTA
250-H020-21-AG3-01
046S004A
draw lead
46
29
2,000
21
250
COTA
250-F030-21-AG3-01
046F003A
fixed
46
29
3,000
21
250
105
95
46
18
10,000
gray
84
vertical
105
95
46
18
10,000
gray
120
vertical
105
95
46
18
10,000
gray
128
vertical
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COTA Technical Specification Sheets
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inch)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance (inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
350-H014-21-AG3-01
069D002A
draw lead
69
44
1,400
21
350
COTA
350-H020-21-AG3-01
069S008A
draw lead
69
44
2,000
21
350
COTA
350-F030-23-AG3-01
069F002A
fixed
69
44
3,000
21
350
160
140
69
27
10,000
gray
110
vertical
160
140
69
27
10,000
gray
175
vertical
160
140
69
27
10,000
gray
182
vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inches)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance. (Inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
550-H014-23-AG3-03
115D002A
draw lead
115
88
1,400
23
550
COTA
550-F020-23-AG3-01
115F001A
fixed
115
88
2,000
23
550
COTA
550-F030-23-AG3-01
115F002A
fixed
115
88
3,000
23
550
260
230
115
42.1
10,000
gray
270
vertical
260
230
115
42.1
10,000
gray
335
vertical
260
230
115
42.1
10,000
gray
580
vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inches)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance. (Inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
650-H014-23-AG3-01
138D002A
draw lead
138
102
1,400
23
650
COTA
650-F020-23-AG3-01
138F002A
fixed
138
102
2,000
23
650
COTA
650-F030-23-AG3-01
138F001A
fixed
138
102
3,000
23
650
310
275
138
50
10,000
gray
318
vertical
310
275
138
50
10,000
gray
454
vertical
310
275
138
50
10,000
gray
615
vertical
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C57.19.01-2000
COTA Technical Specification Sheets
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inches)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance. (Inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
750-H014-23-AG3-01
161D001A
draw lead
161
146
1,400
23
750
COTA
750-F020-23-AG3-01
161F001A
fixed
161
146
2,000
23
750
COTA
750-F030-23-AG3-01
161F002A
fixed
161
146
3,000
23
750
365
315
161
59
10,000
gray
360
vertical
365
315
161
59
10,000
gray
460
vertical
365
315
161
59
10,000
gray
660
vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inch)
BIL (kV)
Withstand 60 Hz
60 s dry (kV)
10 s wet (kV)
Min. Creep Distance (inch)
Min. Arcing Distance (inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
900-H016-23-AG3-01
230D003A
draw lead
230
146
1,600
23
900
COTA
900-F020-23-AG3-01
230F003A
fixed
230
146
2,000
23
900
COTA
900-F030-23-AG3-01
230F005A
fixed
230
146
3,000
23
900
425
350
242.4
84.6
10,000
gray
625
vertical
425
350
242.4
84.6
10,000
gray
838
vertical
425
350
242.4
84.6
10,000
gray
875
vertical
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inch)
BIL (kV)
Withstand 60 Hz
60 s,dry (kV)
Wet switching impulse (kV)
Min. Creep Distance (inch)
Min. Arcing Distance (inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
1175-H016-23-AG3-02
345D002A
draw lead
345
220
1,600
23
1,175
COTA
1175-F020-23-AG3-01
345F001A
fixed
345
220
2,000
23
1,175
COTA
1175-F030-23-AG3-01
345F004A
Fixed
345
220
3,000
23
1,175
520
825
345
94.48
3,300
gray
865
vertical
520
825
345
94.48
3,300
gray
950
vertical
520
825
345
94.48
3,300
gray
980
vertical
10
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COTA Technical Specification Sheets
Type
Style Number
Drawing Number
Current Path (copper)
Insulation Class (kV)
Max. L to G Voltage (kV)
Max. Current Rating (A)
CT Pocket Length (inch)
BIL (kV)
Withstand 60 Hz
60 s,dry (kV)
Wet switching impulse (kV)
Min. Creep Distance (inch)
Min. Arcing Distance (inch)
Max. Altitude (feet)
Color of Porcelain
Approximate Weight (lb.)
Mounting
COTA
1675-F020-23-AG3-01
500F001A
fixed
500
318
2,000
23
1,675
COTA
1675-F030-23-AG3-01
500F005A
fixed
500
318
3,000
23
1,675
COTA
2050-F020-23-AG3-01
765F001A
fixed
765
485
2,000
23
2,050
750
1,175
568.5
149.6
5,000
gray
2,119
vertical
750
1,175
568.5
149.6
5,000
gray
2,120
vertical
920
1,450
765
200
3,300
gray
3,040
vertical
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w w w. t r e n c h g r o u p. c o m
Trench® Austria GmbH
Paschinger Strasse 49
Postfach 13
A-4060 Linz-Leonding
Austria
Phone: 43-732-6793-0
Fax: 43-732-671341
Trench® Limited
Instrument Transformer Division
390 Midwest Road
Scarborough, Ontario
Canada M1P 3B5
Phone: 416-751-8570
Fax: 416-751-6952
Trench® Brasil Ltda
Via Expressa de Contagem, 2685
Contagem, Minas Gerais
CEP 32370-485
Brazil
Phone: 55-31-3391-5959
Fax: 55-31-3391-1828
Trench® France S.A.
16, Rue du Général Cassagnou
B. P. 70 F-68 302
St. Louis, Cedex
France
Phone: 33-3 89-70-2323
Fax: 33-3 89-67-2663
Trench® China
MWB (Shanghai) Co., Ltd
No. 3658 Jiangcheng Road
Minhang, Shanghai,
Peoples Republic of China
200245
Phone: 86-21-54720088
Fax: 86-21-54723118
Trench® Germany GmbH
Nürnberger Strasse 199
D-96050 Bamberg
Germany
Phone: 49-951-1803-0
Fax: 49-951-1803-224
Trench® Fushun
Dong Er Dao, Shuncheng District,
Fushun, Liaoning Province,
Peoples Republic of China
113126
Phone: 86-413-7644009/7644007
Fax: 86-413-7641423
Trench® Limited
Bushing Division
432 Monarch Avenue
Ajax, Ontario
Canada L1S 2G7
Phone: 905-426-2665
Fax: 905-426-2671
Trench® Switzerland AG
Lehenmattstrasse 353
CH-4028
Basel
Switzerland
Phone: 41-61-315-51-11
Fax: 41-61-315-59-00
Trench® (UK) Limited
South Drive
Hebburn
Tyne & Wear
NE 31 1 UW
Phone: 44-191-483-4711
Fax: 44-191-430-0633
Trench® Limited
Coil Product Division
71 Maybrook Drive
Scarborough, Ontario
Canada M1V 4B6
Phone: 416-298-8108
Fax: 416-298-2209
®
Subject to change without notice
04.2003
E322.73
Printed in Canada